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Breathability Discussion

edited by angrysparrow - I split this discussion from the Cuben Fiber thread. This discussion is good, but shouldn't hijack the topic.

Originally Posted by gnome

cuben doesn't breathe,period. However neither does a closed cell pad. and we all use them. I have spent several nights in my cuben Ham. it is fine. The tarp of mine is all taped, and holds up well, for tie outs I use a piece of gorilla tape. the cuben is sandwitched between a single piece doubled back on it self, I then put about 3 stainless ordinary staples to hold (in shear tape is very strong not so strong in peel) cheaper from the manufacturer! my H is abour .44 oz/ yd I believe, stronger than 1.5 or so syl

Gnome, et al,

The prevailing wisdom is that a hammock should be breathable.

Your statemant that we all use closed cell pads is far from accurate...In fact, between Speer pea pods, snug fits, home made UQs and 1/2 UQs, Garlington type taco tubes, Dams, Dam clones, JRB WS and JRB Under Quilts (numbering in the thousands) the majority of folks probably do not use pads. Certainly those who consider themselves back sweaters have moved on from pads.

YMMV... Glad it works for you...

Pan

Last edited by angrysparrow; 08-18-2008 at 10:44.
Reason: added note at top

Ounces to Grams.

www.jacksrbetter.com ... Largest supplier of camping quilts and under quilts...Home of the Original Nest Under Quilt, and Bear Mountain Bridge Hammock. 800 595 0413

I don't know about this 'prevailing wisdom' but I do know that you would like your hammock to be breathable (or at least as breathable as possible with the insulation you are using) when you are overheating and dealing with sweat, or sensible perspiration. On the other hand, I also know that you would like you hammock to not be breathable when you are dealing with trying to stay warm and are only dealing with insensible perspiration-- if you know how to deal with it.

It is not a situation where one case is always the best choice. Wise hammockers that use a breathable hammock with breathable under side insultaion (underquilts, pea pods, etc) often add a vapor barrier between the hammock and the underside insulation to extend the low temperature range. It is like whether to use a tarp that allows air flow or one that closes off and blocks the wind. A nice cool breeze is one thing, a blast of frigid air is something else. Just like a net hammock wouldn't be a wise choice when snow camping, a non-breathable hammock wouldn't be a wise choice when camping in 85F weather. Those are extremes and in the middle range where we typically are, there are shades of gray, so to speak. You will run it to situations where one might be preferred over the other and situations where there isn't that much difference. I wish I could snap my fingers and make my hammock switch back-and-forth between being very breathable to being non-breathable. While I am wishing, it would be nice if I could wave my hand and adjust how my tarp is pitched as well.

i used a sil uq in winter on several occasions, and never experienced moisture build up. and it did make a very noticeable difference in blocking the wind, as i can sometimes feel it through a breathable uq, wheras with the sil uq i never could. i'd say in cool weather and colder, a sil or cuben hammock would perform better than a breathable version, simply because of better protection from wind and water, and would likely allow one to carry a much smaller tarp, particularly if you didn't need to protect your uq.

stevenson's warmlite has some really good info on vapor barriers and how to use them properly for anyone who is interested.

stevenson's warmlite has some really good info on vapor barriers and how to use them properly for anyone who is interested.

Brandon,

I have read that a few times over the years. Jack Stevenson has some good info on vapor barriers and it seems for some reason, that good info on vapor barriers is hard to find. After addressing this subject many times over the years to help people use vapor barriers and to try and overcome misinformation, I have composed my own more generalized write up that I think may be easier to understand. For what its worth, here it is as I posted it on the Yahoo hammockcamping group earlier this year:

My Thoughts on Vapor Barriers... again <grin>

Vapor barriers aren't that easy to use if you don't understand what is
going on and they aren't that hard to use if you do. Does that make
any sense? If it does, you don't need to read any further. If it
doesn't, then read on and I will see if I can help it make sense for you.

I use plastic or silnylon as a vapor barrier between my hammock and my
SnugFit Underquilt. The suspension system on the SnugFit helps keep
the vapor barrier against the fabric of the hammock to minimize air
gaps that would encourage insensible perspiration to condense and
pool. With the vapor barrier held in place against the underside of
the hammock fabric, the hammock fabric wicks away any slight buildup
of insensible perspiration where it can more easily evaporate and I
usually don't even notice it. I pick when I do that and understand
how to use it. It is been very effective for me at extending the
lower temperature range that I can use my underquilt. I would not use
a vapor barrier when I was using the underquilt in warmer conditions
because then I would be dealing with sweat and there would be larger
amounts of sweat/moisture to deal with as the vapor barrier would
cause me to overheat even more and prevent moisture from sweat from
passing through the breathable underquilt.

In general, breathable insulation works best when your insulation is
getting too warm for you and less breathable insulation works best
when your insulation is not quite warm enough for you. That has
everything to do with how, when, and why your body produces sweat (or
sensible perspiration) and insensible perspiration.

Your body produces sweat to help cool off at the outer surface of your
skin with evaporative cooling when you overheat. Your body does not
produce sweat when you are not overheating... you don't just leak
water through your skin all the time. When you are not sweating, your
body can produce insensible perspiration to keep your skin from drying
out. If your skin is moist enough, or not too dry, your body doesn't
produce insensible perspiration because it senses that it doesn't need
to.

It takes energy for your body to produce insensible perspiration.
When you are not overheating and your skin is not producing sweat, a
vapor barrier will cause your skin to quit producing insensible
perspiration after some period of time. Your skin quits producing
insensible perspiration because the vapor barrier creates a high
humidity environment by trapping the moisture from your previous
insensible perspiration. When this happens your body does not use
energy to produce that insensible perspiration anymore and can use
that energy to help keep you warmer. It a sense, your body becomes a
more efficient furnace.

A vapor barrier is not so good when used at the wrong time or when
used incorrectly. When you are overheating and using a vapor barrier,
your skin continually produces sweat as a means of cooling off via
evaporative cooling. The vapor barrier prevents the evaporative
cooling because the sweat is trapped by the vapor barrier. You just
keep sweating and moisture can build up. You need to do something to
keep from overheating because what your body is doing isn't working
because of the vapor barrier. You need to remove the vapor barrier,
vent, or remove insulation.

When you use a vapor barrier with breathable insulation between it and
your skin, that breathable insulation is subject to getting moist or
even wet from insensible perspiration. The insensible perspiration
will initially pass through the breathable insulation and stop when it
hits the vapor barrier. This continues until the humidity builds up
enough for skin to quit producing insensible perspiration. But until
that happens, that breathable insulation is going to be getting moist
too. What you want is a thin wickable sheet of fabric between you and
the vapor barrier such that it can wick any slight moisture buildup
away where it can evaporate into the surrounding air. Of course it
helps for the surrounding air to be able to absorb that moisture
because if it can't, it won't and you will be clammy.

And of course, if you use breathable insulation between you and a
vapor barrier while you are overheating, you will soak that breathable
insulation with sweat (sensible perspiration). That is bad and that
happens when people don't understand how and when to use a vapor
barrier.

Vapor barriers work well for people that know when and how to use them
and are often problems or even disasters for people that don't.

Complicated subjects require complicated explanations. This one is well done. Congratulations.
I found that just reading it left me confused but taking the time to study it was well worth the effort. Thanks for making the effort to share it.